test(cli): expand and reorganize db pull tests

Enhances the test suite for the database pull command by adding comprehensive coverage for common schema features and PostgreSQL-specific functionality.

Includes new test cases for:
- Restoring complex schemas from scratch, including relations and indexes
- Preserving existing imports in multi-file schema setups
- Handling PostgreSQL-specific features like multi-schema support and native enums
- Verifying schema preservation for field and table mappings

The tests are restructured for better clarity across different database providers.

Author: svetch